1. Field of the Invention
The present invention relates to photographic apparatus and more particularly to a self-cocking impact shutter for use in such apparatus.
2. Description of the Prior Art
Photographic cameras having two shutter blades connected by an intermediate spring so that when an impact member moves the first shutter blade to uncover an exposure aperture, the intermediate spring is tensioned to urge the second shutter blade to cover the exposure aperture, are well known in the art. See U.S. Pat. No. 3,661,066 and the above-cited related applications. The above-referenced related applications further disclose the use of a high energy lever to keep the first blade open during the exposure so that the first blade does not rebound to cover the exposure aperture during the exposure. It is also known to employ an electromagnet to hold an armature that is either directly connected to the second blade or connected to an intermediate latch that cooperates with the second blade to hold the second blade open for a time determined by exposure control circuitry and to release the second blade to cover the exposure aperture after the determined time to terminate the exposure. In shutters where the armature is directly connected to the closing blade, the inertia of the closing blade is thereby increased with a consequent increase in the time required to move the closing blade across the exposure aperture thereby rendering the shutter less efficient. In the known shutters employing intermediate latches to hold the closing blade open, the latches have comprised pivotal members which are lightly spring biased so that the armatures carried thereby are moved into contact with the electromagnet when the shutter is cocked to insure positive engagement of the armature with the electromagnet when the electromagnet is energized. Such latches are complicated and therefore costly to manufacture and have associated therewith a characteristic inertia which must be overcome before the closing blade is released. An example of such a latch is shown in U.S. Pat. application Ser. No. 673,515, filed April 5, 1976 in the name of Hochreiter et al., now U.S. Pat. No. 4,059,836. It is also known to cock such two bladed impact shutters by means of a spring connected to the opening blade to urge the opening blade toward an aperture covering position when the high energy lever is cocked. A problem with such an arrangement is that the cocking spring works against the force of the impact member when the shutter is opened thereby requiring a higher force on the impact member for efficient shutter operation.
It is desirable in a two bladed, self-cocking impact shutter to provide means for insuring that the opening blade does not bounce open in the event that the camera is dropped or jarred. It is known to employ a frictional restraint on the opening blade to prevent this type of shutter bounce. Such frictional restraint must be overcome by the high energy lever when the opening blade is opened thereby necessitating a higher force on the impact shutter.